1. Field of the Invention
The invention in general relates to oceanographic instrumentation, and more particularly to a meter for obtaining current velocity and direction.
2. Description of the Prior Art
In oceanographic studies, various sensors are utilized for obtaining oceanographic data. One such sensor or instrument is a fluid current meter which is placed at a fixed geographical point and measures the flow past the point as a function of time. The measurements obtained are utilized, in conjunction with other data to develop an understanding of the kinematics and dynamics which control the circulation in a section of an ocean, river or estuary, for example.
A variety of sensors exists for performing such measurements however many oceanographic studies require a high probability of successful performance over a relatively long deployment, thus ruling out current meters with moving parts exposed to the water environment.
Moving parts are eliminated in acoustic type current meters wherein acoustic transducers are provided for transmitting acoustic pulses toward one another and the difference in the travel time of acoustic pulses due to current, is obtained thereby providing an indication of fluid velocity. Generally two pairs of transducers are utilized with each being contained within a probe, or post. When current flow is in line with two of the posts, an error is introduced into the reading however the error is correctable for that current direction. In reality however the current direction may vary within 360.degree. and unless the current direction is known, proper correction cannot be made to the output reading. Proper correction could be made if a separate sensor which weathervaned with the current were provided but as previously stated one requirement for such meter is that it have no moving parts exposed to the water environment.